Action Points

A systematic review and meta-analysis of randomized clinical trials showed that the use of influenza vaccine in patients at high risk of cardiovascular disease was associated with a lower risk of major adverse cardiovascular events.

Note that the greatest treatment effect was seen among the highest-risk patients with more active coronary disease.

Influenza vaccination was associated with a reduced risk of major adverse cardiovascular events among patients at high risk for heart disease, a meta-analysis showed.

In pooled results from five published, randomized trials, the event rate in the first year of follow-up was 2.9% in those who received flu vaccine and 4.7% in those who didn't (risk ratio 0.64, 95% CI 0.48-0.86), according to Jacob Udell, MD, MPH, of the University of Toronto, and colleagues.

"Influenza vaccination may prevent cardiovascular events via avoidance of atherosclerotic plaque rupture or other forms of cardiac injury in a vulnerable patient and represents a simple, once-annual protective therapy to reduce cardiovascular events," they wrote. "This finding has considerable clinical and health policy importance, given the profound under-use of vaccination among the general public and the potential impact this preventive strategy may have on high-risk patients."

But "future research with an adequately powered multicenter trial to confirm the efficacy of this low-cost, annual, safe, easily administered, and well-tolerated therapy to reduce cardiovascular risk beyond current therapies is warranted," they added.

Steven Lloyd, MD, PhD, of the University of Alabama at Birmingham, told MedPage Today that "this provides the cardiovascular community -- and really all medical professionals -- with even more ammunition to strongly recommend to our patients to get the influenza vaccine."

To address some limitations of prior analyses looking at the relationship between influenza vaccination and cardiovascular risk, Udell and colleagues performed a meta-analysis of randomized trials that compared influenza vaccination with either placebo or no treatment in patients at high risk for cardiovascular disease. They included five published trials and one unpublished trial that included a total of 6,735 patients (average age 67). More than a third of the patients (36.2%) had a history of heart disease.

The meta-analysis showed that influenza vaccination was associated with a reduced risk of events (2.9% versus 4.7%, P=0.003), with a number needed to treat (NNT) of 58 in the pooled results of the published trials and an NNT of eight in the subgroup of patients with a recent ACS.

"Although there will be seasonal variation in those numbers, given the wealth of recently accumulated vaccine safety data, the morbidity associated with new or recurrent coronary disease, and the cost-benefit ratio comparing an inexpensive vaccine to an expensive cardiac event, the decision should be clear," Cameron Wolfe, MBBS, of Duke University, commented in an email to MedPage Today.

"If the results are borne out by real-world experience -- and this will be necessary, given this is simply a meta-analysis and thereby prone to the weaknesses that exist in the underlying studies -- this should leave no doubt in the minds of physicians and patients alike, with any history of cardiovascular disease, that influenza vaccination is the right thing to do," he wrote.

Udell and colleagues acknowledged that the analysis was limited by the relatively small number of cardiovascular events, by differences between the studies in the intended primary outcomes and patient populations, and by various methodological shortcomings of the included trials.

"Although the results of the study ... suggest that influenza vaccine may be associated with a reduced risk of cardiovascular events, as with all meta-analyses, the findings are limited by the quality of the underlying studies and do not imply causation," Kathleen Neuzil, MD, MPH, of PATH in Seattle, wrote in an accompanying editorial.

But "regardless of whether influenza vaccine reduces cardiovascular disease, the known morbidity of influenza in older adults with and without high-risk conditions and the known efficacy of the vaccine warrant its use," she wrote.

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